This invention relates to a blast wheel for use in a rotatable abrading device known as a centrifugal blasting machine or abrasive throwing wheel. More particularly, this invention relates to a blast wheel for propelling abrasive materials at abrading velocities.
In the process of blast cleaning or treating surfaces, such as metal surfaces, with an abrasive grit, shot or sand, the abrasive is propelled by centrifugal force at the surface. This is accomplished by the use of centrifugal blasting machines, which comprise rotors or wheels having a plurality of throwing blades mounted thereon. The blades propel the abrasive against the work surface at very high velocities. Due to the action of the abrasive material on the wheel and the throwing blades, these parts are subject to considerable wear over a period of time. In order to minimize wear, the parts of the machine exposed to the abrasive are generally fabricated from abrasion-resistant alloys or shaped in special configuration to minimize the effects of the abrasive material. Notwithstanding these attempts to minimize wear and extend the life of these machines, periodic removal and replacement of parts is necessary. This results in the loss of valuable operating time.
Another problem associated with centrifugal blasting machines is that the surface of the wheel or rotor, which is opposite the surface on which the blades are mounted, must be finished to close tolerances, such as a few thousandths of an inch. This is because the wheel must be mounted on suitable drive means connected to the shaft of a motor in order to provide movement to the wheel. This is usually accomplished by means of a hub mounted on the motor shaft and bolting of the hub to the finished surface of the blast wheel.
Since the blast wheel is made of an abrasion-resistant material in order to reduce wear caused by exposure to abrasive, it is impractical to machine the rear surface of the blast wheel that is to interface with the hub. Because the material of construction has very good abrasion resistance, it possesses very poor machinability. Therefore, it is necessary to grind the rear surface of the blast wheel, which is a very costly and time-consuming process and not readily adapted to obtaining close tolerances on the finished workpiece.
A third problem encountered with centrifugal blasting machines arises because of the very high speeds at which the blast wheel rotates. Typically, the rotational speed will be between about 1500 and 4000 rpm. It is immediately apparent that the centrifugal wheel must be in dynamic balance in order to prolong its life and prevent damage to the bearings in the drive means to which it is connected.
Thus, there exists a need in the art for a blast wheel for an abrasive blasting machine. The blast wheel should have good resistance to wear caused by exposure to abrasive. The wheel should have readily replaceable parts, especially easily replaceable throwing blades. The blast wheel should also have a surface that can be readily finished in order to interface with a coupling or hub connected to drive means. Furthermore, the blast wheel should be capable of being easily balanced to ensure safe and efficient operation at high rotational speeds in the abrasive blasting machine.